1. Field of the Invention
The present invention relates to well-drilling equipment, and more particularly relates to an arrangement for isolating or patching off troublesome zones in a well.
The present invention can be employed to the utmost effect for patching off troublesome zones in the well drilling process, caused by intense loss of circulation of the drilling mud and cement slurry, by inflows of a liquid or gas from an exposed formation and on account of caving-in or crumbling of the rock being drilled.
2. Description of the Related Art
At present, it has become ever more frequently necessary to drill deep wells for oil and gas production, and more often than not a drilling operation encounters formations which are incompatible from the drilling viewpoint, i.e. have abnormally high and low formation pressures. To provide for further drilling of a well, prior to exposing every successive troublesome formation, the previously drilled part of the well is cased-in with a casing string which is subsequently cemented, and the drilling is resumed with bits of a smaller diameter. The more formations encountered which are incompatible to the drilling conditions, the more casing strings are required. Thus, in order to ensure the required inner diameter of the flow string, it is necessary to start drilling at an overly large diameter which incurs a high energy input into the drilling operation, excessive amounts of casings, cement, labor and time, with the penetration rate slowed down and the drilling operation becoming significantly more costly.
There is known an arrangement for patching off troublesome zones in a well, comprising a casing string whose lowermost part is provided with a shoe and the uppermost part is provided with a packer (M. S. Vinarski, "Sovremennye methody borby s oslozhneniyami pri burenii neftyanykh skvazhin v Tatarii"/Present-Day Methods of Fighting Troubles in Drilling Oil Wells in the Tartar Republic/, 1959, Tatarskoye Knizhnoye Izdatel'stvo (Kazan), pp. 78-80).
A drawback of this arrangement is that its setting considerably reduces the hole diameter, involving the necessity of starting a well with bits of an overly large diameter, to be subsequently decreased in successive steps.
Another shortcoming of the known arrangement is the necessity of cementing it in a well, which incurs excessive inputs of time, cement and electric power.
There is further known an arrangement for patching off troublesome zones in wells (SU, A, 907220), comprising a string of profile pipes with cylindrical portions at their ends, the lowermost end carrying a valve shoe, and the uppermost end having an assembly for joining the profile pipe string to the drill pipes.
The major shortcoming of this known arrangement is that it fails to ensure sufficiently reliable isolation of the formation on account of inadequate sealing of the gap between the arrangement and the borehole wall, and of the joints between the profile pipes themselves. Moreover, if areas of caving-in are present above the zone where the arrangement is set, the rock getting into and beyond the arrangement during the additional round trip required for calibrating the patcher impairs the formation closing-off process, thus impairing the reliability of the isolation of the troublesome zone.
Another shortcoming of the known arrangement is much time required for its setting in the well on account of the necessity of performing additional running and pulling operations involved in calibrating the internal passage of the arrangement, which steps up the drilling costs.
It is an object of the present invention to enhance the reliability of patching off troublesome zones in wells.
It is another object of the present invention to cut the time of setting the arrangement in a well.
It is still another object of the present invention to render the process of patching-off troublesome zones in a well less costly.
The present invention has for its object to create an arrangement for patching off troublesome zones in a well, of a structure which ensures setting of a string of profile pipes in the well in a single round-trip cycle, enhancing at the same time the quality of the sealing-off of the isolated troublesome zones.